Questions

Question 1: Consider the following class:

public class IdentifyMyParts {
    public static int x = 7;
    public int y = 3;
} 

Question 1a. What are the class variables?
Answer 1a: x

Question 1b. What are the instance variables?
Answer 1b: y

Question 1c. What is the output from the following code:

IdentifyMyParts a = new IdentifyMyParts(); 
IdentifyMyParts b = new IdentifyMyParts(); 
a.y = 5; 
b.y = 6; 
a.x = 1; 
b.x = 2; 
System.out.println("a.y = " + a.y); 
System.out.println("b.y = " + b.y); 
System.out.println("a.x = " + a.x); 
System.out.println("b.x = " + b.x); 
System.out.println("IdentifyMyParts.x = " + IdentifyMyParts.x);

Answer 1c: Here is the output:

 a.y = 5 
 b.y = 6 
 a.x = 2 
 b.x = 2
 IdentifyMyParts.x = 2

Because x is defined as a public static int in the class IdentifyMyParts, every reference to x will have the value that was last assigned because x is a static variable (and therefore a class variable) shared across all instances of the class. That is, there is only one x: when the value of x changes in any instance it affects the value of x for all instances of IdentifyMyParts.

This is covered in the Class Variables section of Understanding Instance and Class Members.

Exercises

Exercise 1: Write a class whose instances represent a single playing card from a deck of cards. Playing cards have two distinguishing properties: rank and suit. Be sure to keep your solution as you will be asked to rewrite it in Enum Types.
Answer 1: Card.java

Exercise 2: Write a class whose instances represents a full deck of cards. You should also keep this solution.
Answer 2: See Deck.java .

Exercise 3: Write a small program to test your deck and card classes. The program can be as simple as creating a deck of cards and displaying its cards.
Answer 3: See DisplayDeck.java .